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Paper: Preliminary investigation of period changes of five RR Lyrae stars in the Globular Cluster M15
Volume: 451, 9th Pacific Rim Conference on Stellar Astrophysics
Page: 351
Authors: Li, K.; Qian, S.
Abstract: More than a century of observations of M15 allow us to investigate period changes of RR lyrae stars in it. We find five of them to do deep analysis because period changes of the five are very special and simple polynomials can not fit their O–C diagrams well. The five stars are V11, V13, V15, V40 and V44, respectively. We collect all the times of light maximum from literatures. And then we get our own by observing M15 in November, 2009 using the 60cm telescope in Yunnan Observatory. Base on that we reanalyze period changes of the five stars. We find that all their O–C diagrams can fit by a secular increase or decrease and a cyclic change. If the cyclic changes are caused by the light-travel time effect, they are all in binary systems. Because we could not observe the companion objects from our telescope optically, we think the companion objects are all compact objects, this makes basis for seeking compact objects in Globular Clusters (GCs), and all of the five stars are in the outer region of M15, so this can make some constrains on the evolution of GCs. The five stars are all RR Lyrae stars, so their period changes can also caused by the Blazhko effect and other mechanisms. We should do more observation and discussion to omit the influence of these factors in the future.
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